Hydrogen is currently considered the fuel of the future to facilitate the transition to a low-carbon world. However, most of the hydrogen produced today comes from the reforming of methane, an energy-intensive process that emits large amounts of carbon dioxide. The production of green hydrogen by photocatalysis is an emerging and credible alternative in which solar energy is absorbed by a photocatalyst to break down water into hydrogen and oxygen. However, current photocatalysts, mainly TiO2, have low intrinsic efficiency and noble metals must be used as co-catalysts to improve production efficiencies, significantly increasing the cost of this green hydrogen.
In this project, we propose to develop an emerging material family, High Entropy Oxides (HEOx) as new photocatalysts for the conversion of solar energy into H2. HEOx were discovered recently, in 2015, and are obtained by mixing at least five cations in close equimolar quantities and randomly distributed on the same crystallographic site. Paradoxically, the intrinsic disorder of these systems leads to their stabilization by increasing entropy (ΔS), which becomes predominant before that of enthalpy (ΔH), to minimize free enthalpy (ΔG) (according to the relation ΔG=ΔH-TΔS). The possibilities of cation combinations are almost infinite and the properties of materials can be finely controlled by adjusting compositions and stoichiometers. Optimisation of optical, morphological and photocatalytic properties will be undertaken in the HEROES project, which aims to develop this type of material for hydrogen production.